1. Field of the Invention
This invention relates to a process for producing a transfer member such as an intermediate transfer belt or a transfer belt, used in electrophotographic apparatus in which a toner image formed on a first image-bearing member is electrostatically transferred to a second image-bearing member to obtain an image, and also relates to a transfer member produced by such a production process, and an image-forming apparatus having the transfer member.
2. Related Background Art
Conventionally proposed are full-color image-forming apparatus having a plurality of recording apparatus in which the surface of at least one photosensitive member is exposed to laser beams light-modulated in accordance with recording information to form electrostatic latent images, which are then developed with toners to form toner images, and the toner images formed by development are transferred to a transfer sheet, where the toner images, having different colors, are superimposingly transferred while the transfer sheet is sequentially transported to the respective recording apparatus by means of a transfer member to form full-color toner images, or the different color toner images are superimposingly transferred onto an intermediate transfer member and the resultant full-color toner images are one time transferred to the transfer sheet.
Full-color image-forming apparatuses making use of a transfer belt as the transfer member are so designed that different color toner images are formed on a plurality of photosensitive members and the toner images formed on the respective photosensitive members are transferred, under registration, to one sheet of transfer material being transported in sequential contact with the photosensitive members, to obtain a full-color image.
The full-color image-forming apparatus making use of a transfer belt have an advantage that, a full-color image is formed through one process because the different color toner images are superimposingly transferred while the transfer material is sequentially transported to the respective recording apparatus, so that the images can be formed in a short time.
Meanwhile, compared with image-forming apparatus in which toner images are transferred from a first image bearing member to a second image bearing member transfer material fastened or attracted onto a transfer drum (e.g., Japanese Patent Application Laid-open No. 63-301960), the full-color image-forming apparatus (electrophotographic apparatus) making use of an intermediate transfer member have an advantage that a variety of second image bearing member transfer materials can be selected without regard to their width and length, including thin paper (40 g/m2 paper) and up to thick paper (200 g/m2 paper) such as envelopes, post cards and labels. This is because any processing or control (e.g., the transfer material is held with a gripper, attracted, and made to have a curvature) is not required for the second image bearing member transfer material.
Because of such advantages, full-color copying machines and full-color printers making use of transfer members such as transfer belts or intermediate transfer belts have already begun to be available in the market.
The full-color copying machines and printers making use of such transfer members have various advantages as stated above. On the other hand, they also have some subjects for improvement.
One of them is production cost. These transfer members are required to have various properties such as electrical characteristics, dimensional stability, surface properties and mechanical properties, which must each be controlled strictly. Moreover, any portion which causes a great change in properties even in part makes them unusable. In particular, transfer belts are required to have a surface area larger than image-forming regions and are necessarily large in size. Also, in the case of the apparatus having construction where a plurality of photosensitive members are used, the transfer belt or intermediate transfer member is made to have a large peripheral length because a space for disposing the photosensitive members must be ensured, making it necessary to use a much larger belt member. Accordingly, resistance uniformity, dimensional precision of peripheral length, thickness and so forth and mechanical strength which are required in transfer members are demanded to be on much higher levels. Because of these points, the production of belt members involves a high cost.
Also, with regard to durability, some are not necessarily satisfactory. As a result, this may raise the main-body price and running cost of copying machines and printers and also it may take more labor and time for their maintenance.
Meanwhile, in order to form good full-color images, especially in the case of intermediate transfer belts, some other problems must also be solved which may occur because a plurality of different colors are superimposed on the transfer member.
One of them is a misregistration which may occur between individual colors. In fine lines and character images, even a slight color misregistration tends to be conspicuous to provide a possibility of damaging image quality. When the intermediate transfer belt is used, it must be put over a plurality of shafts, where the tension applied to every part of the intermediate transfer belt is not necessarily uniform when driven and rotated. Hence, the intermediate transfer belt tends to undergo local elongation and, concurrently therewith, may cause a delicately uneven rotation. As the result, a delicate color misregistration may appear when colors are superimposed, as so presumed.
Another problem is occurrence of spots around images. In full-color image formation, superimposing different color toners enlarges the quantity of toner per unit area than in the case of monochromatic images. Especially in characters and fine lines, toners are present in a large quantity on narrow lines. Moreover, individual color toners have electric charges with the same polarity, and hence they are electrostatically repulsive to each other. Thus, it can be said that the toners are on the intermediate transfer belt in an unstable state.
Meanwhile, because of a difference in arcs drawn by the outer surface of the intermediate transfer belt and its inner back surface with belt thickness between them, the difference being produced when the belt passes each shaft about which it is put, the intermediate transfer belt elongates in the peripheral direction at its surface and in the vicinity thereof. Hence, the toner images standing unstable and weak to external disturbance as stated above are disordered because of such surface elongation of the intermediate transfer belt when it passes the shafts, so that the spots around line images come to occur, as so presumed.
Still another problem is transfer performance of halftone toner images. Faulty images tend to occur when the intermediate transfer belt has any uneven electrical resistance or uneven wall thickness.
In addition to these, the intermediate transfer belt, which always undergo tension and repeated bending and stretching stress, is required to have a material stiffness high enough not to cause breakage or cracking of the intermediate transfer belt even in its long-term service.
However, in order to satisfy all of these low cost, high durability and high image quality, technical difficulties are involved. Accordingly, studies are being made on transfer members including intermediate transfer belts, having much superior performances.
In the case of transfer belts, though not the case that images are directly transferred onto the belt, they are also required to have properties comparable to those of intermediate transfer belts in respect of cost reduction, electrical characteristics, surface properties, durability and so forth.
At present, various processes for producing belts and tubes used for transfer members are already known in the art. For example, Japanese Patent Application Laid-open No. 3-89357 and No. 5-345368 disclose a process for producing a semiconducting belt by extrusion. Japanese Patent Application Laid-open No. 5-269849 also discloses a process in which a belt is obtained by joining both ends of a sheet to bring it into a cylindrical form. Japanese Patent Application Laid-open No. 9-269674 still also discloses a process in which a belt is obtained by forming a multi-layer coating film on a cylindrical substrate and finally removing the substrate. Meanwhile, Japanese Patent Application Laid-open No. 5-77252 discloses a seamless belt obtained by centrifugal molding.
The above processes each have merits and demerits. For example, in the extrusion, setting the die gap of an extruder die in the same size as the desired belt thickness involves considerable difficulties for producing thin-layer belts that can achieve the cost reduction and can make the spots around line images occur less frequently, tending to cause uneven wall thickness and uneven electrical resistance affected by such thickness. In the case when both ends of a sheet are joined, the difference in height and decrease in tensile strength at the joint come into question. Still also, processes making use of solvents as in cast molding, coating and centrifugal molding require many steps of preparing a coating solution, coating it and removing the solvent, resulting in a high cost.
As a process for producing an endless belt which is thin-gauge and has no fold, Japanese Patent Applications Laid-open No.1-228823 and No. 4-255332 disclose a process in which an extruded tube is brought into contact with a cooling mandrel so provided as to be held inside the extruded tube, its size is adjusted there, and, after it has been hardened, it is held between nip rolls also disposed inside and outside the tube and then taken off while it is kept tubular. Japanese Patent Application Laid-open No. 5-50490 also discloses a production process in which a sizing sleeve is provided on the outside of a tubular film.
In these processes, however, a size adjustment mechanism attached to the production apparatus comes into contact with an extruded product to adjust the size, and hence a problem may arise such that no smooth extrusion can be carried out in the case of resins having a large coefficient of friction or resins having a high melting temperature which may harden rapidly. Hence, tough materials commonly having high modulus of elasticity and breaking strength tend to obstruct the improvement in strength of the belt because of their high melting temperature.
In the process in which the size is adjusted in contact with the tube surface, the surface of the belt produced is also finely scratched to undesirably adversely affect image characteristics in some cases. Also, in these processes, it is difficult to obtain extruded products greatly larger than circular dies, and is difficult to take any means for sufficiently drawing an extruded product in the direction perpendicular to the direction of extrusion to improve the strength of the extruded product.
In addition, when the size of a product is changed, it is necessary to remake the size adjustment mechanism of course and even the circular die, to bring about various problems of, e.g., equipment cost increase, which causes a raise of product price.
Accordingly, the present inventors propose a process for producing a novel transfer member that is different from any conventional ones, having solved the above problems, and to provide a transfer member obtained by the process and an image-forming apparatus having the transfer member.
An object of the present invention is to provide a process for producing a transfer member at a lower cost, in a smaller number of steps and in a rich variety of forms.
Another object of the present invention is to provide a process for producing a transfer member which can be free of any changes in its size and characteristics and can maintain characteristics at the same level as those at the initial stage even when used repeatedly to make severe running service.
Still another object of the present invention is to provide a process for producing a transfer member which can contribute to the formation of good full-color images having less color misregistration and less spots around line images.
A further object of the present invention is to provide a process for producing a transfer member having a superior dimensional precision of thickness, peripheral length and so forth of belts.
A still further object of the present invention is to provide a transfer member obtained by the above production process, and an image-forming apparatus having the transfer member.
That is, the present invention provides a process for producing a transfer member to be used in a transfer system by which a toner image formed on a first image-bearing member is transferred to a second image-bearing member; the process comprising the steps of;
melt-extruding an extrusion material from a circular die of an extrusion/forming apparatus into a cylindrical film; and
measuring the circumference of the cylindrical film and sending the resultant information to the extrusion/forming apparatus to adjust the circumference of the cylindrical film.
The present invention also provides a transfer member to be used in a transfer system by which a toner image formed on a first image-bearing member is transferred to a second image-bearing member; the transfer member comprising a cylindrical film obtained by;
melt-extruding an extrusion material from a circular die of an extrusion/forming apparatus into a cylindrical film; and
measuring the circumference of the cylindrical film and sending the resultant information to the extrusion/forming apparatus to adjust the circumference of the cylindrical film.
The present invention still also provides an image-forming apparatus having the above transfer member.